This invention relates to a method and apparatus for optically reading out previously recorded signals on an optical disc by way of data reproduction. In an optical disc reproducing device for reading out and reproducing recorded signals on the optical disc used as a disc-shaped recording medium, an optical pickup device is employed for optically reading out the recorded signal. This optical pickup includes laser outputting means, made up e.g., of a laser diode, and is configured for condensing and illuminating the laser light outgoing from the laser outputting means on the optical disc and for receiving the light reflected from the optical disc for outputting the received reflected light as electrical signals by way of reading out the pre-recorded signals as RF signals.
At the same time as the pre-recorded signals are read out, servo error signals in the vertical direction and in the tracking direction of the optical pickup with respect to the optical disc are outputted as focusing error signals and as tracking error signals, respectively. As the recorded signals are read out, focusing servo and tracking servo are carried out using the focusing error signals and the tracing servo signals. For the case in which the optical disc presents significant warp, it is contemplated to perform skew servo for controlling the tilt of the optical axis the optical pickup with respect to the optical disc.
For stable readout of the pre-recorded signals, it is necessary to maintain the respective servo gain values in a pre-set range. On the other hand, it is also necessary to set the converging positions of the laser light beams at an optimum position for signal readout during the respective servo operations.
On the other hand, since the servo error signals employed in these servo operations, such as focusing error signals or tracking servo signals, are produced by monitoring the light reflected by the optical disc, it may occur that these servo error signals are fluctuated under the effect of optical disc fluctuations or temperature changes in the optical pickup. These fluctuations tend to change the gain or offset of the servo error signals, this producing variations in the servo gain values or converging positions.
However, the effect of the fluctuations in the servo gain or offset has so far not been taken into consideration.
Heretofore, if servo error signals are fluctuated within the optical disc during data reproduction from the optical disc, or if variations are produced in the servo error signals due to temperature changes in the optical disc reproducing apparatus, the servo gain or offset is changed thus rendering stabilized data reproduction impossible.